1. Field of the Invention
The present invention relates to a micro mirror and a method of manufacturing the same, and more particularly, to a micro mirror having a reflecting plane with an accurate angle and shape and a method of manufacturing the same by coating the reflecting plane of a micro mirror formed by isotropic wet etching of silicon with a polymer and pressing the polymer using a mold with a predetermined angle and shape accuracy.
2. Description of the Related Art
Micro mirrors can be used for optical pickups, optical communication systems, optical information processing systems, etc. An optical data storage device using an optical pickup records/reproduces information to/from an optical disc. Optical discs are distinguished from other data storage devices by the advantages of ease of distribution, portability, high capacity, copy protection, etc.
To achieve a high recording density by collecting optical energy to a small spot, an optical data storage device recording and reproducing data to and from an optical disc has been developed for a decreased wavelength of a light source and an increased numeral aperture (NA) of an objective lens. For example, an optical data storage device for a compact disc (CD) uses a light source having a wavelength of 780 nm and an objective lens having an NA of 0.45, and an optical data storage device for a digital versatile disc (DVD) uses a light source having a wavelength of 650 nm and an objective lens having an NA of 0.6.
Recently, with the trend of adapting an optical disc for a portable information device, a micro optical pickup has been under active development. Conventionally, to miniaturize an optical pickup and an optical data storage device using the same, the entire volume of an optical system is usually reduced by decreasing the size of optical elements. However, this size reduction has a technological limit. Considering this limit, there has been an attempt to use semiconductor manufacturing processes to manufacture optical pickups. Conventionally, when optical elements that are several millimeters in size are assembled, a large amount of time is needed to individually adjust the optical elements to an optical axis. Therefore, the automation rate of the optical elements is low. However, when optical pickups are manufactured using semiconductor processes, they can be manufactured at a wafer level, and therefore, mass production is possible. In addition, this method facilitates miniaturization, assembly, and adjustment of the optical elements.
FIGS. 1A through 1D are sectional views of stages in a method of manufacturing a micro mirror using semiconductor processes, which is disclosed in U.S. Patent Publication No. 2001/0048548.
Referring to FIG. 1A, a silicon wafer 10 is prepared by cutting a silicon ingot 9.74° off-axis with respect to a <111> direction from a (100) plane, using Miller indices. The silicon wafer 10 has a thickness of about 500 μm. Etch masks 21 and 22 are formed on opposite sides of the silicon wafer 10.
Referring to FIG. 1B, an etch window 23 is formed in the etch mask 21 on a front surface of the silicon wafer 10 using photolithography.
Referring to FIG. 1C, wet etching is performed by putting the silicon wafer 10 with the etch window 23 in an isotropic silicon etchant such as KOH or TMAH maintained at an appropriate temperature. After a predetermined period of time of the wet etching, planes respectively having slant angles of 45° and 64.48° with respect to a bottom surface of the silicon wafer 10 are formed. Reference numeral 12 denotes one plane of four (111) crystal planes appearing when etching is stopped.
Referring to FIG. 1D, after removing the etch masks 21 and 22, the silicon wafer 10 is cut to use a 45-degree slant plane 11.
The above-described micro mirror can be manufactured at a wafer level, and satisfactory plane accuracy can be obtained when a light source having a long wavelength is used or an etch depth of the optical elements is low. However, when an etch depth is greater than several hundreds of micrometers, it is difficult to lower a surface shape accuracy below λ/6, which is usually required for optical elements of an optical pickup, for example, below about 70 nm in a blue-ray optical disc using a short wavelength of 405 nm, with the conventional method of manufacturing a micro mirror. To manufacture a high precision mirror, a high-quality silicon wafer that is cut toward an accurate crystal direction and has an extremely low impurity concentration should be used. Moreover, since etching conditions such as the concentration, temperature, and agitation of an etchant and an etching apparatus must be precisely controlled, manufacturing cost naturally increases.